Author: Prof Joop Boomker

Infections of the gastro-intestinal tract

Helminths of the oesophagus and forestomach

The Gongylonema species, of which there are several, occur in the submucosa of the tongue, oesophagus or the rumen. The typical zig-zag pattern in the mucosa is the only indication of the presence of the worms. They are non-pathogenic (Fig. 5).

Like the Gongylonema species, adult Calicophoron, which live in the rumen and reticulum, are non-pathogenic (Fig. 6). Several species occur in wildlife, all of which use a freshwater snail, usually of the genus Bulinus, as intermediate host. Briefly, the life cycle is as follows: Eggs are released with the faeces and must be freed from the faeces, i.e. when they fall into water, before they hatch. The miracidia must enter the host within 3 hours of hatching or they will die. In the snails, the miracidia form sporocysts, then rediae, daughter and granddaughter rediae. The granddaughter rediae produce cercariae which leave the snail, and form metacercariae on the surface of the water or on vegetation. When ingested by the host, they excyst in the small intestine. After 15 to 50 days they migrate up the small intestine, through the various stomachs to end up in the rumen where they develop into the adult flukes.

Fig. 5: The zig-zag worm, Gongylonema, in the mucosa of the oesophagus

Fig. 6: Adult Calicophoron microbothrium, visible as pink globules hidden between the papillae in the rumen

Helminths of the abomasum

With the exception of the Parabronema spp., the helminths that occur in the abomasum have monoxenous life cycles.

A number of Haemonchus species occur in the abomasum of antelopes, but their pathogenicity has not been studied. From several surveys in the Kruger National Park (KNP) and in some of the KwaZulu-Natal Parks (KZNP) it became apparent that certain Haemonchus species are associated with certain host groups. For example, in the KNP and KZNP, Haemonchus vegliai (Fig. 7) is associated with the browsing antelope (kudu, nyalas and bushbuck) while impalas in the KNP harboured Haemonchus krugeri (Fig. 8). In areas where game and domesticated ruminants graze the same pastures, for example, sheep and blesbok or impalas, the game will harbour Haemonchus contortus, the primary Haemonchus of sheep. This has economic and managerial implications since the wild ruminants can act as reservoir hosts for resistant H. contortus.

Fig. 7: The tips of the spicules of Haemonchus vegliai from kudus

Fig. 8: The tips of the spicules and gubernaculum of Haemonchus krugeri from impalas

Fig. 9: Haemonchus vegliai in the abomasum of a kudu

Deaths of sable and roan antelopes and kudus because of resistant H. contortus infections are known. In all cases the clinical signs and gross pathological lesions were the same as for similar infections in sheep

Teladorsagia, Ostertagia and Longistrongylus all belong to the subfamily Ostertagiinae, and all produce more or less the same kind of lesions in their antelope hosts (Figs. 10 & 11). The lesion is essentially a nodular abomasitis, caused by hyperplasia of the mucosa, which in turn is caused by the nematodes that develop and live in the abomasal glands (Pletcher, Horak, De Vos & Boomker, 1984). The helminths have been described from a variety of antelopes and no adverse effects because of the infection have been seen. Basson, Kruger & McCully (1968, cited in Basson, McCully, Kruger, Van Niekerk, Young, De Vos, Keep & Ebedes, 1976) however, saw fatal cases of ostertagiosis caused by Ostertagia ostertagi in eland that were kept in small camps.

Fig. 10: Nodules caused by Ostertagia ostertagi in the abomasum of an eland

Fig. 11: Nodules caused by Longistrongylus sabie in the abomasum of an impala from the Kruger National Park (arrow)

Fig. 12: Lateral view of the spicules of Trichostrongylus thomasi

Fig. 13: Lateral view of the spicules of Trichostrongylus axei

Trichostrongylus thomasi (Fig. 12) is the species usually found in the abomasum of a number of antelope species and it is the counterpart of Trichostrongylus axei (Fig. 13) of domesticated ruminants. This author has neither seen clinical signs nor has he seen lesions as a result of the presence of this parasite.

Different species of Parabronema (Fig. 14) parasitize elephants, rhinoceroses, buffaloes and giraffes in South Africa, and of camels, sheep, cattle and buffaloes in North Africa. All make use of a stomoxid fly, Haematobium or Lyperosia, as intermediate host. The fly larva ingests eggs or first stage larvae of the nematode. The nematode larvae develop to the second stage in the fly larva, and have developed to the infective third stage by the time the fly emerges from the pupa. The fly has to be ingested, either with water or food for the life cycle to continue. Large numbers of worms are often present in the abomasum or stomach, and may or may not cause gastric ulcers.

Fig. 14: Parabronema skrjabini in an ulcer in the stomach of an elephant.
The lesions in giraffe are very similar.

Helminths of the small intestine

Although immature Calicophoron (= Paramphistomum) spp. (Fig. 15) cause serious disease in susceptible domestic animals, clinical disease has, to the best of my knowledge, not been described in antelope in South Africa, although recently a case in nyalas occurred in the North West Province. This case occurred in animals kept in an enclosure and the intermediate hosts were present in the water supply, a trough.

The strongylid nematode Agriostomum (Fig. 16) occurs in the posterior part of the small intestine, where it on occasion produces ecchymoses on the mucosa. Despite the worms being fairly often encountered, the life cycle is unknown and no clinical signs or pathology have been described.

Fig. 15: Immature Calicophoron collected by washing faeces from an affected animal through a sieve

Fig. 16: Dorsal view of the head of Agriostomum gorgonis, a parasite of blue wildebeest and kudus

The family Trichostrongylidae is well represented in all antelope and the commonly encountered genera are Cooperia, Cooperiodes, Nematodirus, Impalaia, Paracoperia and Trichostrongylus. As is evident from Table 5, there are numerous species of especially Cooperia and Trichostrongylus.. Large numbers of worms of any or all the genera mentioned above can occur in antelope, but clinical signs are rarely seen.

Bunostomum trigonocephalum was present in 3 out of 12 impalas culled at Pafuri in the KNP, and all three were approximately 8 months old. Neither showed any clinical disease or macroscopic lesions (Boomker & Horak, unpublished data). Small numbers of Gaigeria pachyscelis have been recorded from blue wildebeest in the KNP, and mostly in the 4-12 month old antelopes, again without clinical signs or macroscopic lesions (Horak et al., 1983).

Moniezia benedeni and Moniezia expansa as well as Avitellina are widely spread in antelope throughout southern Africa, but no clinical disease has been recorded. These tapeworms are usually seen in young animals.

Helminths of the large intestine

Oesophagostomum is a large genus of which two species are commonly encountered in antelopes. These are Oesophagostomum columbianum (Fig. 17) and Oesophagostomum walkerae. The former nematode species has been recorded from at least 18 antelopes, but no mention is made on the pathogenicity of the parasites in their respective hosts.  Oesophagostomum radiatum is fairly common in buffaloes in the KNP but the infection is mild (Basson et al., 1970). The nodules that are commonly seen in sheep and goats, and even cattle, are much less conspicuous in antelope.

Several species of the genus Trichuris parasitize wildlife. Trichuris globulosa, one of the more commonly encountered species, occurs in 8 antelope species. It is, however, a rare finding in buffaloes and the infection is invariably very mild (Basson et al., 1970), as it is in the majority of antelopes. Because of its monoxenous life cycle, and the infective larva that occurs in a thick-walled egg, large numbers can build up in enclosures and under intensive conditions. In private collections or zoos, this parasite is one of the most troublesome.

Fig. 17: A piece of large intestine with the nodules that is so characteristic of
Oesophagostomum infections in ruminants.